Permethrin is a synthetic pyrethroid which exhibits repellent as well as knockdown and kill activity against insects. Pyrethroids, including both the naturally occurring compounds and their synthetically prepared analogs effectively control a variety of pests, such as ticks, cockroaches, houseflies, mosquitoes, and other flying or crawling insects. Pyrethroids are not harmful to plants, food, animals or humans, and leave no harmful residues.
Despite these highly favorable characteristics, permethrin has had only limited general utility because of its relatively short-lived insecticidal activity. This is due to the decomposition of permethrin into a nonactive, non-insecticidal product in the presence of oxygen and ultraviolet light.
Pat. No. 5,198,287 issued Mar. 30, 1993 to Samson, et al. for INSECT REPELLENT TENT FABRIC teaches a tent fabric with a water repellent and flame retardant coating that includes the insecticide permethrin with an effective life of more than six months. Placing the permethrin in the coating for the inner surface of the tent is a major factor in the longevity of the permethrin in tents made in accordance with the '287 patent.
U.S. Pat. No. 5,252,387 issued Oct. 12, 1993 to Samson for FAB-RICS WITH AN INSECT REPELLENT AND A BARRIER teaches that permethrin can be preserved in insect repellent fabrics by placing a barrier over the permethrin to protect the permethrin from degradation by ultraviolet light and oxygen.
Another problem with using permethrin as an insect repellent in washable end items is retaining the permethrin in washable end items through successive wash cycles.
U.S. Pat. No. 5,089,298 issued Feb. 18, 1992 to McNally for SYNERGISTIC EFFECT OF AMYLOPECTIN-PERMETHRIN IN COMBINATION ON TEXTILE FABRICS offers one solution to the problem of retaining permethrin in end items through successive wash cycles. McNally teaches that permethrin is retained in garments impregnated with permethrin and amylopectin, a water soluble form of starch, through a substantially greater number of laundering cycles than garments treated only with permethrin.
Subsequent to the issuance of the foregoing patents, research has continued for effective use of permethrin in repelling mosquitoes and other insects. The importance of the continued research is demonstrated by the more than 50,000 casualties, due to malaria, that the U.S. Army suffered during the Vietnam conflict (Navy Medical Guide, 1984).
Applicants' research, to date, has shown that another synergist, polyvinylacetate, is more effective than amylopectin for the retention of permethrin in fabric through successive wash cycles. The fabric used during applicants' tests is a washable fabric intended for use as various end items, including garments.
McNally impregnates completed garments with amylopectin and permethrin--not the fabric from which the end items is made. Applicants treat the fabric, during its manufacture, with polyvinylacetate and permethrin, which is less expensive and more efficient than treating individual end items with permethrin and a synergist.